A few years ago, Bill Gross, America’s “bond king” and the manager of the world’s largest mutual fund, was on a mat doing his daily yoga session, when an idea came to him. Instead of just following the crowd and investing in subprime loans, he decided to take 10 of his employees, dispatch them across the country posing as home buyers, and “take the temperature” of America’s housing market.

A year or so later, they came back with some shocking news; homes were being bought without a down payment or without any proof of income; ridiculous amounts of money were being lent to people who never had a hope of paying the money back. In short, there was a housing bubble in America that was just about to burst.

As a result, Gross decided not to invest in the subprime mortgage market. And the moral of the story? First, have the courage of your convictions. Two, do your research. And three, practise yoga.

It wouldn’t be every executive’s first choice. Yoga, once the preserve of scrawny men in drawstring trousers meditating on top of a mountain, has, since the Nineties, turned itself into a spirit-lite way for women with Gucci mats and Sweaty Betty vest tops to keep fit and tone their bums, tums and thighs. In the past three or four years, however, an increasing number of people from the top echelons of business, finance and politics, looking to get an edge over their rivals or manage their stress levels, have been following Gross’s lead and adding a yoga instructor to their retinue of chefs, nannies and personal trainers.

Suddenly, it’s not only acceptable for alpha males to do yoga; it’s considered by many to be a badge of honour. Billionaire investor Guy Hands, the British chairman of EMI, is a fan. So too are Peter Mandelson (who’s admitted a penchant for “hot” Bikram yoga) and Rahm Emanuel, President Obama’s former chief-of-staff. Russell Simmons, the multimillionaire founder of the hip hop label, Def Jam, does a one-and-a-half hour yoga workout every day and Steve Jobs, the founder of Apple, was a devotee of the Indian guru Paramahansa Yogananda. When he died last month, it’s claimed the only book Jobs had downloaded on his iPad 2 was Yogananda’s Autobiography Of A Yogi.

“These are very competitive guys,” says John Capouya, author of the book Real Men Do Yoga. “Everyone is smart, everyone works a million hours a day and they do yoga to give them a mental sharpness. They think, ‘I’ll trade bonds better and I’ll make more money than the other guy if I do it.’”

If anything, today’s uncertain economic climate has meant it’s even more important to have something extra in your armoury.

Gross, who practices at 8.30am every day at a hotel across the street from his office in California, credits yoga with giving him the focus and clarity of thought to sift through the hubbub of noise that swirls around the financial markets. Some of his best ideas, he told the New York Times in 2009, come when he’s standing on his head.

“Very ambitious, high-achieving people realise that there’s something in yoga that is useful to them,” says instructor Tara Fraser, who, with her partner, Nigel Jones, runs the Yoga Junction studio in north London. “It’s not weird, not hippy. If you’re a man, the fact that you do yoga shows that you’re in touch with your intuitive side and you’re flexible as well as strong.

“If you said, ‘No, no, no. I don’t want to do any of that stuff, I just want to work out at the gym and build muscle’, I think, nowadays, people would think, ‘Hmm. What are you trying to prove?’

“Yoga shows that you’re a well-rounded individual. You know how to choose the wine, you know which restaurants to go to. Adding yoga to your portfolio of skills impresses people.”

One yoga-practising head of human resources I’ve heard about, at a very large law firm, looks for yoga on applicants’ CVs and, if two candidates are more or less equally qualified, recommends the yoga enthusiast over his or her rival.

In New York, the yoga capital of the Western world, the studio is fast replacing the private members’ club, or golf club, as the place to be seen or steal “face time” with people who you want to impress or give you a job. It’s not unheard of for hedge funders to hear a rival has been spotted doing a Downward Dog and immediately sign up for lessons, for fear they might be losing some sort of advantage.

But aren’t all these high-flyers missing the point? What about the philosophy? When it was first devised, more than 5,000 years ago in India, yoga was a technique to attain perfect spiritual insight and tranquility. The Indian Gnostic scriptures, the Upanishads (which include the text most known to Westerners, the Bhagavad Gita), state that all humans are members of a single family. We are all one. It certainly wasn’t devised as a weapon with which to make yourself rich and crush your enemies.

Simon Low, one of the most in-demand instructors in Britain, is himself a refugee from the corporate world; a former vice president of RCA records, who turned to yoga for salvation after burning out in the Nineties. His client list features celebrities and CEOs and he is happy to admit that many of them use yoga to inflate their incomes.

“The journey of yoga is towards creating a calmer, more focused mind,” he says. “Nowhere in yoga does it tell you that you cannot have wealth. It’s what you do with it and how you acquire it that matters. It’s how you behave as a human being to yourself and in your community and the world as a whole. Suggesting that you have to go to a monastery and give up everything is an option but it’s not one that is the [central] path of yoga.”

The monastery is certainly not where one of yoga’s most famous proponents, Bikram Choudhury, is heading any time soon. The inventor of “hot yoga”, in which students sweat it out in temperatures of 40C, he owns a fleet of 40 Rolls-Royces and Bentleys and has been estimated by The Wall Street Journal to be worth $7 million. Other “elite” teachers, such as David Life and Sharon Gannon (the co-founders of Jivamukti yoga) and Shiva Rea, make a small fortune from running super exclusive retreats and selling books and DVDs, and many are flown around the world by their rich clients who want their own private yoga tutor on tap while they’re on holiday.

In fact, the yoga industry is proving so profitable (it’s currently valued at $42 billion) that an increasing number of people are packing in their City jobs and going into yoga themselves.

James Muthana, the founder of Yogaat.com, an agency that provides instructors to blue chip companies, is a former investment banker. “People who are very focused on their careers in their twenties often get to their early thirties and want something more,” he says. “Fifteen years ago, they were looking at IT start-ups, 10 years ago, property, and now, a large number are looking at yoga, pilates and meditation.

“My instructors have very impressive CVs. Some were ad executives, some worked in management consulting and quite a few worked in investment banking. Most of us started doing yoga by chance and, over time, noticed when we did it we were more positive, energetic and decisive.”

Paul Silver, a private banker-cum-broker for what the financial world calls “high net worth individuals”, keeps his yoga mat and belt at his office and has a private lesson at the beginning of each week. (“I don’t like to be surrounded by people who are better than me,” he explains.) His teacher, Ailon Freedman, is under strict instructions not to preach any yoga mumbo-jumbo, but Silver admits that, almost without realising, he has changed. He’s calmer than he was before and more focused.

“Unless you’re a genius, life is really about discipline in my opinion,” he says. “And by its very definition, there are not many geniuses around. So you have to conform to certain disciplines and yoga is basically that. You have to follow a routine, do something on a regular basis and do it properly. It’s very purposeful.”

It’s also proven to relieve stress. It can be no coincidence that yoga has become popular among bankers and businessmen at a time when stock markets are in their most tumultuous state since the 1930s. Add to that the relentless march of technology and the constant bombardment of emails, tweets and status updates, and you can see why people are desperate to carve out some private space for themselves.

“We were never designed to be as stimulated in as many different ways for such long periods of time as we are today,” says Oliver Patrick, a physiologist at Viavi, a health care company set up by the luxury concierge service, Quintessentially. “Our clients sometimes travel through four time zones during the course of a week. They work 14 or 15 hour days and are permanently contactable. That’s an extremely occupied mind.”

For an annual subscription of upwards of £9,500 a year, Viavi’s clients can have their saliva analysed for the level of the stress hormone cortisol and their heart beat measured at night, via two ECG electrodes, to ascertain the quality of their sleep. After a period of doing yoga, the clients do the tests again and show a marked improvement in sleep and a decrease in cortisol levels

Of course, some people are beyond help. “Occasionally you get someone who just shouts at you, ‘I’ve got 45 minutes to relax’,” says Yoga Junction’s Tara Fraser. “Like, make me beautiful or make me this or that. And you just think, ‘Oh for goodness’ sake. If that’s your attitude it’s not going to work.’” Another teacher says she once had a client, a billionaire, who used to turn up at every class with three mobile phones, all on different time zones.

“When a lot of these guys come in, their eyebrows are glued together, their brows are furrowed and their shoulders are hunched forward,” says Tara Stiles, a New York-based instructor. “Then they put their coat on somebody else’s coat. They step on somebody’s shoes. There’s just a lack of simple body awareness. They’re standing in the middle of the doorway when someone else is trying to get in and they don’t even realise someone’s behind them.”

Stiles, a former model who has recently released a series of DVDs with Jane Fonda, doesn’t have much time for the ancient yogic teachings. At her massively popular studio in SoHo, she likes to cut straight to the asanas – the postures. But she’s keen to stress that doesn’t mean something “meaningful” can’t happen to you in her class.

“When you do yoga, you’re actually dealing with all your problems on a more subconscious, intuitive level. It’s not like a psychoanalyst where you talk about things. Nobody’s telling you how to feel. It’s all coming from inside. You just feel like being a nicer person. You feel like giving.”

But it doesn’t work on everyone. Emails disclosed earlier this year in a lawsuit brought by a Canadian insurance company featured some choice language by Daniel Loeb, a multi-millionaire hedge fund manager who has been practising yoga for many years and is married to a former yoga instructor. Loeb, who was betting on the shares of the company Fairfax Financial tumbling in price, described the company’s CEO, Prem Watsa, as a “schwartza”, a derogatory term for a black man in Yiddish, and wrote another email to a consultant saying, “Die, Prem, die”. Not very yoga.

Fraser laughs. “If you’re a real bad apple to start with, I don’t think yoga is going to cure you,” she says. “I think you might just remain a bad apple. It’s not a magic wand.”